Conventional methods for detecting thunderstorms use radio waves created by lightning. These systems include antennas that detect radio frequency (RF) emissions from lightning to determine the occurrence and position of lightning associated with thunderstorms. A computerized electronic system determines the direction and distance between the lightning strikes and the aircraft. The lightning strikes are then depicted on a display that shows the relative position of the aircraft to the lightning strikes (i.e. thunderstorm). For example, see Ryan (U.S. Pat. No. 4,023,408) for a description of a lightning display system known as "Stormscope" and Markson (U.S. Pat. No. 4,972,195) for a description of an improved lightning range system.
In a conventional lightning display system for an aircraft, the display shows an aircraft symbol and the location of the lightning strike with respect to the aircraft. The aircraft operator can select the range in which lightning strikes will be displayed. The lightning strike depiction remains on the display after the strike is over so that a collection of these strikes depicted in a particular area indicates that a thunderstorm is present.
Conventional systems have certain drawbacks. For example, when the aircraft turns, the depicted lightning strike appears in the same relative position it had with the aircraft when the strike occurred and not the new relative position it has with the aircraft on the new heading. A method commonly employed to compensate for this shortcoming is to connect and correlate the lightning detection system to the aircraft heading indicator so that as the aircraft turns, the lightning display is rotated an equal number of degrees in order to maintain the same angular relationship between the aircraft and the strike.
Another shortcoming of the prior art is that as the aircraft moves, the lightning strike depiction maintains the same relative positional or distance relationship with the aircraft that existed when the strike occurred and not the true positional relationship with the aircraft in its new location.